Have Cat Questions? Ask a Cat Vet Online.
Hello and thanks for trusting me to help you and your pet today. I am a licensed veterinarian with over 25 years experience and would be happy work with you.
Based on the picture that you have provided, I would tell you that this would looks pretty deep. Since the fight happened a week ago, it is most likely that this may have formed an abscess that ruptured open and that is why it was not noted right away until after it did. There appear to be healthy granulation tissue that is trying to form as it tries to heal from the inside out, but if this was an abscess, there can be a large pocket of dead space where the abscess was and there could be unhealthy tissue there that needs to be debrided or it will just allow adjacent tissue to become infected. It sounds as if you are doing a good job of keeping it clean, and it is possible that it could heal on it's own, but your best bet would be to at least have him examined and have the site evaluated to see if there is more infection underneath the skin. He may need to have that cleaned up or at the least allow it to close on it's own but get some antibiotics on board. That should be fairly inexpensive and if you ask for a prescription, many antibiotics are available at human pharmacies for a very low cost or free.
Here are some other resources that may help you to help him.
petsmart free visit: http://www.banfield.net/exclusiveoffer/
Care credit (veterinary): http://www.carecredit.com/vetmed/
I hope this is helpful. Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please reply so I can clarify for you.